You can also submit new features request and vote for them.
Is it possible to specify a link text (alias) for a link in sequence diagrams like the following in creole markup?
It's not possible in the official release, but with last beta https://dl.dropboxusercontent.com/u/13064071/plantuml.jar
You can have:
Bob -> Alice: [[http://www.google.com foo]]
Is this what you are expecting ?